I'm looking for a solution to have a version column on my table based on another column.
I have a column "document No" in my table. Every time I insert a new row with the same document no, I would like to increase the column version.
I know I can it by the back-end. But, it means I have first to read the table and then insert. My idea is to optimize the performance and leave it with SQL Server.
Is It possible?
pk DocNo Version
---------------------
1 ABC 0
2 CBD 0
3 ABC 1
4 FGH 0
5 ABC 2
Assuming that you can parameterize your query (as in a stored procedure), AND your primary key is set to IDENTITY, you can use something along the lines of:
INSERT INTO TableA (DocNo, Version)
(SELECT TOP 1 'XYZ',ISNULL(MAX(Version)+1,0)
FROM TableA WHERE DocNo = 'XYZ')
I used 'XYZ' where you would place your parameter like:
INSERT INTO TableA (DocNo, Version)
(SELECT TOP 1 #DocNo,ISNULL(MAX(Version)+1,0)
FROM TableA WHERE DocNo = #DocNo)
Stored Procedure Solution
CREATE PROCEDURE tableUpsert(#DocNo varchar(100))
AS
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
BEGIN TRAN
IF EXISTS(SELECT * FROM dbo.YourTable WITH (UPDLOCK) WHERE DocNo = #DocNo)
UPDATE dbo.YourTable
SET Version = Version + 1
WHERE DocNo = #DocNo;
ELSE
INSERT dbo.YourTable(DocNo, Version)
VALUES(#DocNo, 1);
COMMIT
Code is pretty self-explanatory. If the record exists, you update by incrementing your VersionNumber column and if it doesn't, then insert a new record with default VersionNumber of 1. Note the use of UPDLOCK to ensure that only your specific process is currently updating the record.
You can use insert trigger. In the trigger, update the Version by getting last version of same DocNo and increment by 1.
update t
set Version = isnull(v.Version, 0) + 1
from inserted i
inner join mytable t on i.pk = t.pk
outer apply
(
select Version = max(Version)
from mytable x
where x.DocNo = i.DocNo
) v
Your version number is implicit in your data. Use the PK to determine it via
SELECT DocNo, ROW_NUMBER() over (PARTITION BY DocNo ORDER BY pk) as version order by DocNo when you retrieve the data (or put that in a view)
Relying on IDENTITY may give you gaps
Relying on MAX(x)+1 may not always work depending on your concurrency model.
Locking the table/column will introduce concurrency issues (which may be unimportant or trivial in your case).
Related
I have two SQL Server tables called Table A and Table B. I have an application which inserts one row into Table A and three rows into Table B at the same time. As you can see in the screenshot below, we can link these inserted records based on their ID column in Table A and TransID column in Table B.
During the data insert on table B, if any rows out of 3 inserted rows contain a value called Printed in the Printed column, I want to update my Table A's relevant record's PrintStatus column to Printed as well.
How do I write a SQL Server trigger for this?
Well the best solution is to do this in your code(app) but if there is no way,
you can write a Trigger After Insert for Table B like the trigger example below:
CREATE TRIGGER [dbo].[YourTrigger] ON [dbo].[TableB]
AFTER INSERT
AS
DECLARE #id INT
BEGIN
SET NOCOUNT ON;
SET #id = (SELECT DISTINCT ID FROM Inserted)
IF EXISTS (SELECT * FROM Inserted WHERE Printed='Printed')
UPDATE TableA
SET PrintStatus='Printed'
WHERE ID = #id
END
May this help you
It could be correct for your problem : (not sure at 100%)
CREATE TRIGGER TriggerTableB
ON TableB
AFTER INSERT
AS
UPDATE TableA AS A
SET PrintStatus = 'Printed'
WHERE A.TranID = inserted.ID
AND 'Printed' = (SELECT MAX(I.Printed)
FROM inserted AS I)
I would recommend querying for the information:
select a.*,
(case when exists (select 1
from b
where b.id = a.tranid and b.printed = 'Printed'
)
then 'Printed'
end) as printstatus
from a;
This is simpler than writing a query and you can wrap this in a view.
From a performance perspective, an index on b(id, printed) should make this pretty fast -- and not slow down inserts.
A trigger can be quite complicated, if you want to take inserts, updates, and deletes into account. I prefer to avoid such complication, if possible.
I am facing a problem and cant find any solution to this. I have a source table (T) where I get data from field. The data may contain duplicate records with time stamp. My objective is to take the field data and store it into a final table (F) having the same structure.
Before inserting I check whether key field exists or not in the F if yes I update the the record in F with the latest one from T. Other wise I Insert the record in F from T. This works fine as long as there is no duplicate record in T. In case T has two records of the same key with different time stamp. It always inserts both the record (In case the key is primary key the insert operation fails). I am using following code for the operation -
IF EXISTS(SELECT * FROM [Final_Table] F, TMP_Source T WHERE T.IKEy =F.IKEY)
begin
print 'Update'
UPDATE [Final_Table]
SET [FULLNAME] = T.FULLNAME
,[FATHERNAME] = T.FATHERNAME
,[MOTHERNAME] = T.MOTHERNAME
,[SPOUSENAME] = T.SPOUSENAME
from TMP_Source T
WHERE Final_Table.IKEy = T.IKEy
and [Final_Table].[RCRD_CRN_DATE] < T.RCRD_CRN_DATE
--Print 'Update'
end
else
begin
INSERT INTO [Final_Table]
([IKEy],[FTIN],[FULLNAME],[FATHERNAME],[MOTHERNAME],[SPOUSENAME]
)
Select IKEy,FTIN,FULLNAME,FATHERNAME,MOTHERNAME,SPOUSENAME
from TMP_Source
end
The problem comes when I my T table has entries like -
IKey RCRD_CRN_DATE ...
123 10-11-2013-12.20.30
123 10-11-2013-12.20.35
345 10-11-2013-01.10.10
All three are inserted in the F table.
Please help.
Remove all but the latest row as a first step (well, in a CTE) using ROW_NUMBER() before attempting to perform the insert:
;WITH UniqueRows AS (
SELECT IKey,RCRD_CRN_DATE,FULL_NAME,FATHER_NAME,MOTHER_NAME,SPOUSENAME,FTIN,
ROW_NUMBER() OVER (PARTITION BY IKey ORDER BY RCRD_CRN_DATE desc) as rn
FROM TMP_Source
)
MERGE INTO Final_Table t
USING (SELECT * FROM UniqueRows WHERE rn = 1) s
ON t.IKey = s.IKey
WHEN MATCHED THEN UPDATE
SET [FULLNAME] = s.FULLNAME
,[FATHERNAME] = s.FATHERNAME
,[MOTHERNAME] = s.MOTHERNAME
,[SPOUSENAME] = s.SPOUSENAME
WHEN NOT MATCHED THEN INSERT
([IKEy],[FTIN],[FULLNAME],[FATHERNAME],[MOTHERNAME],[SPOUSENAME]) VALUES
(s.IKEy,s.FTIN,s.FULLNAME,s.FATHERNAME,s.MOTHERNAME,s.SPOUSENAME);
(I may not have all the columns entirely correct, they seem to keep switching around in your question)
(As you may have noticed, I've also switched to using MERGE since it allows us to express everything as a single declarative statement rather than writing procedural code)
If I create a VIEW using this pivot table query, it isn't editable. The cells are read-only and give me the SQL2005 error: "No row was updated. The data in row 2 was not committed. Update or insert of view or function 'VIEWNAME' failed because it contains a derived or constant field."
Any ideas on how this could be solved OR is a pivot like this just never editable?
SELECT n_id,
MAX(CASE field WHEN 'fId' THEN c_metadata_value ELSE ' ' END) AS fId,
MAX(CASE field WHEN 'sID' THEN c_metadata_value ELSE ' ' END) AS sID,
MAX(CASE field WHEN 'NUMBER' THEN c_metadata_value ELSE ' ' END) AS NUMBER
FROM metadata
GROUP BY n_id
Assuming you have a unique constraint on n_id, field which means that at most one row can match you can (in theory at least) use an INSTEAD OF trigger.
This would be easier with MERGE (but that is not available until SQL Server 2008) as you need to cover UPDATES of existing data, INSERTS (Where a NULL value is set to a NON NULL one) and DELETES where a NON NULL value is set to NULL.
One thing you would need to consider here is how to cope with UPDATES that set all of the columns in a row to NULL I did this during testing the code below and was quite confused for a minute or two until I realised that this had deleted all the rows in the base table for an n_id (which meant the operation was not reversible via another UPDATE statement). This issue could be avoided by having the VIEW definition OUTER JOIN onto what ever table n_id is the PK of.
An example of the type of thing is below. You would also need to consider potential race conditions in the INSERT/DELETE code indicated and whether you need some additional locking hints in there.
CREATE TRIGGER trig
ON pivoted
INSTEAD OF UPDATE
AS
BEGIN
SET nocount ON;
DECLARE #unpivoted TABLE (
n_id INT,
field VARCHAR(10),
c_metadata_value VARCHAR(10))
INSERT INTO #unpivoted
SELECT *
FROM inserted UNPIVOT (data FOR col IN (fid, sid, NUMBER) ) AS unpvt
WHERE data IS NOT NULL
UPDATE m
SET m.c_metadata_value = u.c_metadata_value
FROM metadata m
JOIN #unpivoted u
ON u.n_id = m.n_id
AND u.c_metadata_value = m.field;
/*You need to consider race conditions below*/
DELETE FROM metadata
WHERE NOT EXISTS(SELECT *
FROM #unpivoted u
WHERE metadata.n_id = u.n_id
AND u.field = metadata.field)
INSERT INTO metadata
SELECT u.n_id,
u.field,
u.c_metadata_value
FROM #unpivoted u
WHERE NOT EXISTS (SELECT *
FROM metadata m
WHERE m.n_id = u.n_id
AND u.field = m.field)
END
You'll have to create trigger on view, because direct update is not possible:
CREATE TRIGGER TrMyViewUpdate on MyView
INSTEAD OF UPDATE
AS
BEGIN
SET NOCOUNT ON;
UPDATE MyTable
SET ...
FROM INSERTED...
END
I use a cursor to iterate through quite a big table. For each row I check if value from one column exists in other.
If the value exists, I would like to increase value column in that other table.
If not, I would like to insert there new row with value set to 1.
I check "if exists" by:
IF (SELECT COUNT(*) FROM otherTabe WHERE... > 1)
BEGIN
...
END
ELSE
BEGIN
...
END
I don't know how to get that row which was found and update value. I don't want to make another select.
How can I do this efficiently?
I assume that the method of checking described above isn't good for this case.
Depending on the size of your data and the actual condition, you have two basic approaches:
1) use MERGE
MERGE TOP (...) INTO table1
USING table2 ON table1.column = table2.column
WHEN MATCHED
THEN UPDATE SET table1.counter += 1
WHEN NOT MATCHED SOURCE
THEN INSERT (...) VALUES (...);
the TOP is needed because when you're doing a huge update like this (you mention the table is 'big', big is relative, but lets assume truly big, +100MM rows) you have to batch the updates, otherwise you'll overwhelm the transaction log with one single gigantic transaction.
2) use a cursor, as you are trying. Your original question can be easily solved, simply always update and then check the count of rows updated:
UPDATE table
SET column += 1
WHERE ...;
IF ##ROW_COUNT = 0
BEGIN
-- no match, insert new value
INSERT INTO (...) VALUES (...);
END
Note that this approach is dangerous though because of race conditions: there is nothing to prevent another thread from inserting the value concurrently, so you may end up with either duplicates or a constraint violation error (preferably the latter...).
This is just psuedo code because I have no idea of your table structure but I think you will understand... basically Update the columns you want then Insert the columns you need. A Cursor operation sounds unnecessary.
Update OtherTable
Set ColumnToIncrease = ColumnToIncrease + 1
FROM CurrentTable Where ColumnToCheckValue is not null
Insert Into OtherTable (ColumnToIncrease, Field1, Field2,...)
SELECT
1,
?
?
FROM CurrentTable Where ColumnToCheckValue is not null
Without a sample, I think this is the best I can do. Bottom line: you don't need a cursor. UPDATE where a match exists (INNER JOIN) and INSERT where one does not.
UPDATE otherTable
SET IncrementingColumn = IncrementingColumn + 1
FROM thisTable INNER JOIN otherTable ON thisTable.ID = otherTable.ID
INSERT INTO otherTable
(
ID
, IncrementingColumn
)
SELECT ID, 1
FROM thisTable
WHERE NOT EXISTS (SELECT *
FROM otherTable
WHERE thisTable.ID = otherTable.ID)
I think you'd be better off using a view for this -- then it's always up to date, no risk of mistakenly double/triple/etc counting:
CREATE VIEW vw_value_count AS
SELECT st.value,
COUNT(*) AS numValue
FROM SOME_TABLE st
GROUP BY st.value
But if you still want to use the INSERT/UPDATE approach:
IF EXISTS(SELECT NULL
FROM SOMETABLE WHERE ... > 1)
BEGIN
UPDATE TABLE
SET count = count + 1
WHERE value = #value
END
ELSE
BEGIN
INSERT INTO TABLE
(value, count)
VALUES
(#value, 1)
END
What about Update statement with inner join to perform +1, and Insert selected rows that do not exist in the first table.
Provide the tables schema and the columns you want to check and update so I can help.
Regards.
Is there any way to update a table within the select_expr part of a mysql select query. Here is an example of what I am trying to achieve:
SELECT id, name, (UPDATE tbl2 SET currname = tbl.name WHERE tbl2.id = tbl.id) FROM tbl;
This gives me an error in mysql, but I dont see why this shouldn't be possible as long as I am not changing tbl.
Edit:
I will clarify why I cant use an ordinary construct for this.
Here is the more complex example of the problem which I am working on:
SELECT id, (SELECT #var = col1 FROM tbl2), #var := #var+1,
(UPDATE tbl2 SET col1 = #var) FROM tbl WHERE ...
So I am basically in a situation where I am incrementing a variable during the select statement and want to reflect this change as I am selecting the rows as I am using the value of this variable during the execution. The example given here can probably be implemented with other means, but the real example, which I wont post here due to there being too much unnecessary code, needs this functionality.
If your goal is to update tbl2 every time you query tbl1, then the best way to do that is to create a stored procedure to do it and wrap it in a transaction, possibly changing isolation levels if atomicity is needed.
You can't nest updates in selects.
What results do you want? The results of the select, or of the update.
If you want to update based on the results of a query you can do it like this:
update table1 set value1 = x.value1 from (select value1, id from table2 where value1 = something) as x where id = x.id
START TRANSACTION;
-- Let's get the current value
SELECT value FROM counters WHERE id = 1 FOR UPDATE;
-- Increment the counter
UPDATE counters SET value = value + 1 WHERE id = 1;
COMMIT;